It is known in the prior art for a train vehicle to be operating along a roadway track divided into signalling blocks of predetermined lengths, with a low impedance connection being provided between the track rails at the end of each such signalling block. A signal transmitter is operative with one end of each signal block at one of several frequencies and a cooperative signal receiver is coupled with the other end of each signal block for controlling the operation of a train vehicle positioned within that signal block such as described in U.S. Pat. No. Reissue 27,472 and U.S. Pat. No. 3,532,877 of G. M. Thorne-Booth and in U.S. Pat. No. 3,593,022 of G. M. Thorne-Booth et al. A published article entitled "Automatic Train Control Concepts Are Implemented by Modern Equipment" was published in the September, 1972 Westinghouse Engineer at pages 145 to 151 and disclosed this operation of a train vehicle.
The train vehicle carried a signal receiver which sensed a desired input command speed coded signal within the signal block occupied by that vehicle and which input command speed signal was decoded to provide a desired speed command signal to the propulsion control apparatus of the vehicle to result in energizing the propulsion motors for regulating the actual speed in accordance with the desired speed of operation along the track and within each signal block. If the actual speed of the vehicle is too low, more propulsion effort is required and if the actual speed is too high, then braking of the vehicle is required. A propulsion enable signal is provided to the vehicle propulsion and brake system when the actual speed of the vehicle is less than the desired speed for that vehicle within a given signal block. When the actual speed of the vehicle is greater than the desired speed, then the propulsion enable signal is not provided and the full service brake will be applied. For the train vehicle to move along the roadway track, it must be out of full service brake condition of operation to move in response to a desired speed signal.
It was known in the prior art to provide brake assurance to validate that the vehicle is properly responding to the decelerating request, as set forth in an article published in the Conference Record of the 12th annual meeting of the IEEE Industry Applications Society, Los Angeles, Calif., October 1977. Problems which can cause improper response include brake system failure or loss of traction. If brake system failure is the primary concern then the vehicle response can be measured to a limited degree by wheel deceleration. If traction loss is to be detected, then a slip-slide system can measure the loss.
It is known in the prior art to provide a speed control system employing redundancy techniques to achieve a high degree of failsafety and speed control accuracy. For this purpose, two tachometers producing signals proportional of vehicle speed and two substantially identical signal processing channels are provided for redundancy, with one signal channel responding to a desired speed ONES input signal and the other signal channel responding to a desired speed ZEROS input signal. Each such signal processing channel produces an output speed error signal equal in magnitude but opposite in polarity from the output speed error signal of the other channel when the system is operating properly. The speed output error signal from each channel is applied to respective level detectors which provide control signals to an alarm and braking apparatus for braking the vehicle or train the vehicles whenever an overspeed condition is sensed. The signal outputs of the two channels are compared and when they are not of the same magnitude indicating a failure in one or possibly both of those channels, an alarm is actuated again and the vehicle is braked. The speed error signal outputs of the two signal processing channels are summed and the mean value of the resultant summation is used as a speed error signal for controlling the drive motors of the vehicle during the time an overspeed condition is not sensed, as described in U.S. Pat. No. 3,749,994 of T. C. Matty.
It was known in the prior art to use an accelerometer carried by a transit vehicle in the form of a pendulum which was operative to release the brake effort of the vehicle if too much braking of the vehicle resulted in too rapid stopping of the vehicle for the comfort of the passengers. In this regard, a switch was connected with the pendulum and was opened to release the brakes when the pendulum swung too far from the center position.
A general description of microprocessors and the related peripheral devices suitable for the practice of the present invention is provided in the Intel 8080 Microcomputer Systems Users Manual currently available from Intel Corp., Santa Clara, Calif. 95051.